Baylor College of Medicine (BCM) is a new applicant for continuation of the Womens and Infants Transmission Study (WITS) in the form of WITS Il. At the time of the application for WITS I in 1987, there was neither a suitable patient population in Houston nor an organized center for conduct of natural history studies of HIV-infected women and their infants. Since that time, however, a large maternal-infant population infected with HIV has been identified and a highly organized and efficient National Institutes of Health (NIH)-Pediatric-Obstetrical HIV Research Center has been formed by BCM and the University of Texas Medical School in Houston (UT). BCM-UT now seeks to perform WITS II research as part of its coordinated recruitment of HIV-infected mother-infant pairs into natural history, diagnostic, and therapeutic clinical trials programs. By using the combined strengths of other NIH grants and contracts plus the facilities of the general Clinical Research Center (GCRC) at the BCM- affiliated Texas Children's Hospital, it will be possible to enroll 50 mother-infant pairs per year into WITS II with a greater economy of effort and financial resources than otherwise would be possible. Specifically the BCM-UT WITS Il unit will recruit 50 HIV-infected mother-infant pairs into a 4-year natural history study of the effects of HIV on pregnant women and their infants. Additionally, WITS II will attempt to answer certain specific research questions, such as whether natural factors influence the incidence of vertical HIV transmission. This research question is based on the hypothesis that maternal factors such as depressed immunity (e.g. low CD4+ cell counts), contribute to an enhanced HIV mother-to-infant transmission rate. Moreover, WITS II will add to its original goals by determining the natural history of HIV infection in pregnant women and their infants who have been exposed to antiretroviral agents, prophylactic agents, and immune-based therapies. By recruiting annually at least 50 HIV-infected mother-infant pairs from a largely minority inner city disadvantaged population, BCM-UT will make a substantial contribution to the national WITS II program and enable it to meet its goals of understanding the natural history of HIV disease in the United States.